The present invention relates to a twist drill, particularly a drill made entirely of hard metal and having major flanks ground in by a cut which produces helical faces. References herein to hard metal as the preferred material also include the use of a sintered or compound material, at least as the cutting material.
It is generally known that the helical grinding of a drill face in the vicinity of the chisel, or cutting, edge results in a greater clearance angle. This is favorable for easy, centered spot drilling but not favorable for high feed rates, particularly since it weakens the chisel edge. Thus, in order to improve cutting conditions in twist drills having helically ground faces corrections are often made at the chisel edge, e.g. by making it pointed or by adapting the side rake angle to the material to be drilled, as disclosed in Stock-Taschenbuch by R. Stock AG [Handbook published by the R. Stock AG], Berlin, 3rd Edition of 1979, at page 40.